A computer glitch during Sydney's New Year's Eve fireworks spectacular left thousands of harbour revellers wondering why a central barge had stopped firing pyrotechnics for a heart-stopping half-minute.

The breakdown occurred about halfway through the 12-minute midnight show, and left the barge - just to the east of the Harbour Bridge and one of seven set up for the display - in the dark for many long seconds.

With about 1.5 million people crammed into vantage points along the harbour, the sudden halt was noticed by many onlookers, who wondered whether something had gone wrong.

''With all the planning that goes into these events, you don't expect something like that to happen,'' said Alex Isiais, from Lindfield, who was watching with a group of friends at Cremorne Point.

''My first thought was that it was intended but then it went on for too long.''

The event's fireworks director, pyrotechnist Fortunato Foti, attributed the hitch to the barge's coordinating computer going down.

"The computer pretty much runs the fireworks and, of course, sometimes things with computers go wrong, so we always have a back-up,” he said.

The barge was firing again after the pause and Mr Foti said the hiatus had not detracted from the entertainment.

“The reports are that everyone had a great time," he said. "If they're happy, we're happy."

Nearly 100 people were charged on the night by police for offences including drug supply, assault and offensive behaviour, although police praised the overall good behaviour of revellers.